166 SYMBIOGENESIS 



life, or if all alike have become impoverished because tending 

 in the anti-biotic direction. It is difficult to see, apart from 

 this, how any of them can be "actually injurious," although 

 Darwin thinks that " we may feel sure that any variation in 

 the least degree injurious would be rigidly destroyed" (by 

 natural selection). 



Prof. G. Henslow absolutely denies that Nature develops 

 seedlings with any " injurious," i.e., " inadaptive," varia- 

 tions (according to Darwin's requirement). 



As we have recognised that there occur frequent compati- 

 bilities of unions of a retrogressive order, we must again con- 

 clude that what genuine genetic antagonism is exhibited by 

 certain variations round the mean of a "character " is due to 

 opposite bio-economic tendencies, which, of course, express 

 themselves also in opposite physiological tendencies and that 

 a reliable standard of utility or of " injuriousness " can be 

 obtained only on bio-economic lines. 



We have also recognised that the fertilisation process 

 itself is to some extent a safeguard against impurities and 

 impedimenta, although even its good offices, like those of 

 digestion, may become obliterated by abuse. 



That Mendelian segregation constitutes a third line of 

 defence, as it were, of racial purity is quite possible. It is 

 essential for bio-economic reasons that the relatively 

 higher and more valuable variations assert themselves against 

 the relatively lower and less valuable (which, as we have 

 seen, may easily have become the carriers of disease). 



Before there can be any alternative inheritance at all, be 

 it remembered, there must be a previous evolution of alterna- 

 tive " characters." Although, as Dr. Walker says, no two cells 

 are ever precisely alike (which in Spencer's parlance makes 

 variation co-extensive with heredity), their mere unlikeness 

 affords no presumption of a fruitful or permanent and viable 

 cross. Something more than this unlikeness is necessary, viz., 

 something complementary and mutually advantageous in their 

 respective characteristics. It is this which gives the oppor- 



